The present invention relates to a shift control system for an automatic transmission.
U.S. Pat. No. 4,680,992 issued to Hayasaki et al., on July 21, 1987 discloses a shift control system for an automatic transmission. This known shift control system comprises a 3-2 timing valve, an overrunning clutch control valve, a shuttle valve, and a solenoid. The solenoid generates a solenoid pressure under the control of a control unit. The shuttle valve communicates with the timing valve, overrunning clutch control valve, and solenoid. It comprises a valve spool or valve element movable responsive to a line pressure that is variable with the engine throttle opening (viz., engine load) between a first position where the overrunning clutch control valve is under the control of the solenoid pressure while the 3-2 timing valve is not under the control of the solenoid pressure, and a second position where said overrunning clutch is not under the control of the solenoid pressure while the 3-2 timing valve is under the control of the solenoid pressure. The automatic transmission of this type is described in a publication "NISSAN FULL-RANGE AUTOMATIC TRANSMISSION RE4R01A TYPE, SERVICE MANUAL, (A261 C07) issued on Mar.1987 by Nissan Motor Co., Ltd.
An object of the present invention is to provide an automatic transmission provided with a hydraulic control system wherein a plurality of valves are controlled by a solenoid without any valve therebetween.